In a typical silent chain, a number of inner link plates, each having a pair of teeth and a pair of pin holes, are arranged in interleaved relationship in alternate “guide” link rows and non-guide link or “joint” link rows, extending widthwise of the chain. The guide link rows have guide plates at both ends, so that guide plates are provided along both sides of the chain. The alternate guide link rows and joint rows are connected articulably by connecting pins to form an endless loop. Typical silent chains of the type referred to above are shown and described in U.S. Patent Application Publication 2003/0195074 and U.S. Pat. No. 6,733,410.
FIGS. 2(A) and 2(B) show an example of a conventional silent chain 21. Similarly shaped inner link plates 24a and 24b constitute the inner link plates of guide link rows GL, which have guide plates 26 at their outer ends. The plates of the guide link rows GL are interleaved with link plates 25a and 25b of joint link rows JL. As shown in FIG. 2(B), each link plate has a pair of teeth 22 and a pair of pin holes 23. The guide plates 26 do not have teeth. The interleaved rows Gl and JL are connected by connecting pins 27, which fit into pin holes 28 of the guide plates 26 so that the pins are fixed to the guide plates. However, the pins fit into the pin holes 23 of these inner link plates 24a, 24b, 25a and 25b with a clearance.
Since the inner link plates are arranged in alternate interleaving rows, when a joint link row has a number n of link plates (four in the example shown), the number of link plates plus the number of guide plates in a guide link row is n+1 in the plates (inner link plates 25a and 25b) arranged in the non-guide link row and a total number of n+1 (five in the example shown).
When a longitudinal tensile load F is exerted on the chain during operation, as shown in FIG. 3, the load is divided among the inner link plates and the guide plates. However, since the number of plates (26, 24a, 24b, 24a, 26) in the guide link row GL is different from the number of plates (25a, 25b, 25b, 25a) in the joint link row JL, the loads applied to the respective plates become unbalanced.
Since connecting pins 27 are fixed in pin holes of the guide plates 26 at the ends of the guide link rows GL, and fit into pin holes 23 of the inner link plates (24a, 24b, 25a, 25b), when a tensile load F is exerted, the connecting pins 27 are bent, and the guide plates 26 are flexed as shown in FIG. 3. As a result, stress is not applied to all the inner link plates uniformly. Instead, stress is concentrated on specific inner link plates, namely plates 25a, which are adjacent the guide plates 26 and positioned at the outermost ends of the joint link rows JL, and a relatively low stress is applied to the intermediate link plates 25b in the joint rows.
The bending of the link plates also causes a high load to be applied to the inner link plates 24b, which are central link plates in the guide link rows GL. However, a relatively low load is applied to the inner link plates 24a, which are positioned near the guide plates 26.
The bending of the connecting pins thus results in unbalanced tensile loads on the link plates, and the stress balance is made even worse because the guide link rows and the joint rows have different numbers of plates.
The high load applied to certain link plates, especially link plates 25a, results in excess surface pressure acting on the inner circumferential surfaces of the pin holes 23 in these link plates, and on the outer circumferential surfaces of the connecting pins 27. Consequently both the inner surfaces of the pin holes and the outer surfaces of the connecting pins tend to wear rapidly, causing chain elongation.
Since the chain is composed of interleaved plates arranged alternately in the direction of the width of the chain, if each guide link row GL is composed of five plates (26, 24a, 24b, 24a, 26) and each joint link row JL is composed of four plates (25a, 25b, 25b, 25a) the plates contact one another at eight locations across the width of the chain, giving rise to a significant friction loss as the chain articulate when moving around sprockets.
In use, portions of outermost plates 25a of the joint link rows JL tend to fracture, and the measured wear of link plates 25a is significantly greater than the wear of the intermediate link plates 25b. 
Accordingly, an object of this invention is to overcome the above-mentioned problems encountered in conventional silent chains. More specifically, an objects of the invention is to provide a silent chain in which, when a tensile load is exerted in the longitudinal direction of the chain, stresses applied to the respective inner link plates of the chain are made as uniform as possible, the high degree of wear in the pin holes of specific link plates and of the portions of the connecting pins in those pin holes, is suppressed, chain wear elongation is reduced, and link plate surface wear, caused by movement of the link plates against one another, is decreased.